The present invention relates generally to power equipment, and particularly to chain saws used for cutting material.
A chain saw includes a powerhead and a guide bar about which a saw chain is entrained. A portion of the chain rests slidably within a groove about the periphery of the guide bar. The saw chain includes cutting links extending outward from the guide bar and drive tangs extending into the groove and positioned for engagement by a drive sprocket of the powerhead to move the saw chain about the guide bar during cutting operations. As the saw chain engages a work piece, operational forces develop tension within the saw chain as the drive sprocket urges the chain into movement and the work piece resists such movement. These operational forces can be particularly acute at the guide bar nose, i.e. the distal end of the guide bar, and represent a potential for damage to the guide bar.
To more broadly distribute operational forces imposed upon the guide bar, saw chains include nose sprockets. The nose sprocket mounts rotationally at the guide bar nose and includes teeth adapted to engage the tang portions of the saw chain. The nose sprocket may be implemented as an outer bearing race coupled by a roller bearing set to an inner bearing race affixed to the guide bar. As the saw chain moves about the guide bar, the nose sprocket rotates and lifts the chain away from the guide bar at the guide bar nose. Operational forces developed at the guide bar nose bear against the nose sprocket rather than directly upon the guide bar rails. The nose sprocket thereby delivers these forces, in distributed fashion, to the guide bar through the bearing arrangement.
Saw chain technology has taught that the nose sprocket gullets, i.e. space between sprocket teeth for receiving the chain drive tang, should be oversized at their base relative to the drive tangs of the saw chain. Saw chains have included asymmetric formations at the tips of the drive tangs for clearing the guide bar groove and maintaining lubricant movement. An oversized region at the base of the gullet accommodates the asymmetric configuration of these drive tang tips. The drive tang engages the nose sprocket in wedge-like fashion, i.e. the tang contacts the sprocket at two points along the upper portion of the gullet, i.e., at the sides of the adjacent sprocket teeth.
More recently, saw chain technology has been applied to aggregate cutting, but aggregate cutting places greater wear and stress on the saw chain relative to that of wood cutting applications. Much of saw chain technology applicable to wood cutting applications cannot be directly applied to aggregate cutting. For example, the development of aggregate cutting chain saws first overcame the extraordinary wear conditions imposed upon the saw chain as it engaged the abrasive aggregate workpiece. As more durable aggregate cutting saw chains became available, other components of the chain saw demonstrated failure under the harsh, extreme stress conditions of aggregate cutting. Among such components is the nose sprocket.
The present invention provides a guide bar nose sprocket particularly suitable for the extreme stress conditions of aggregate cutting applications.